IRSN, Institut de radioprotection et de sûreté nucléaire

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Enhancing Nuclear Safety



Risk informed approach for the safety analysis of French nuclear power plants

J.M. Lanore,
PSAM - 8th International Conference on Probabilistic Safety Assessment and Management, New Orleans, USA, May 14-19, 2006,
Rapport DSR N° 126


  This paper describes the role of risk insights in the safety analysis of French Nuclear power plants.
Although the regulatory position is and remains deterministic, the probabilistic approach takes an increasing place in the safety decisions. Despite a limited regulatory framework, in fact the risk insights are more and more taken into consideration as a supplement to the traditional deterministic demonstration.
France holds a rather unique position with a large, highly standardized reactor fleet, build by a single constructor and operated by a single operator. This situation has provided favourable conditions for the application of PSAs to power reactors since the 80s, explaining also the rather not prescriptive regulation, which is more a continuous technical dialogue between the regulators and the operators.
The presentation gives some views on the position of the French regulators (ASN), in particular on the following issues:
usefulness and limitations of PSAs probability-based safety criteria ASN considers that PSAs are useful tools for assessing safety, but that one must remain aware of their limitations, like scope restriction and uncertainties. Probabilistic results are always to be used as a supplement to other safety considerations, and preferably in relative terms. In order to clarify the acceptable approach, the regulators have requested the writing of a Basic Safety Rule on “development and utilisation of probabilistic safety assessments”.
Regarding the second item, ASN considers that probabilistic objectives can be used as orientation values but not as regulatory limits. This is done in particular for the EPR project. Generally speaking ASN’s policy is to regularly increase safety, and for that purpose Safety Objectives have not to be defined in probabilistic terms (the compliance is very difficult to demonstrate and they could have a negative effect by limiting the safety efforts when the objectives are met).
This position can be illustrated by the description of some PSA applications for safety improvements. In particular for the plants in operation PSA is an important part of the periodic safety reviews and recently, for the third periodic safety review of the 900 MWe PWR series, PSA level 1, Fire PSA and PSA level 2 were considered as useful supplements to the traditional analysis. Practical examples of applications are given. The use of PSA for the safety demonstration of the future project EPR is also indicated.

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